Hearing aids are wearable hearing devices that serve to assist hearing-impaired persons. Hearing aids exhibiting different structural designs such as behind-the-ear (BTE), in-the-ear (ITE) and concha hearing aids etc. are provided for meeting individual requirements that are many in number. The hearing aids cited by way of example are worn on the outer ear or in the auditory canal, but the market also offers bone-conduction, implantable and vibrotactile hearing aids in the case of which impaired hearing is stimulated either mechanically or electrically.
Hearing aids basically have as their essential components an input converter, an amplifier, and an output converter. The input converter is as a rule a sound receiver, for example a microphone, and/or an electromagnetic receiver, for example an induction coil. The output converter is implemented usually as an electroacoustic transducer, for example a miniature loudspeaker, or as an electromechanical converter, for example a bone-conduction earphone. The amplifier is customarily integrated in a signal processing unit. This basic structure is shown in FIG. 1 using a behind-the-ear hearing aid as an instance. Built into a hearing aid housing 1 for wearing behind the ear are one or more microphones 2 for receiving ambient sound. A signal processing unit 3 that is likewise integrated in the hearing aid housing 1 processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is conveyed to a loudspeaker or earphone 4 that feeds out an acoustic signal. The sound is conveyed to the hearing aid wearer's eardrum possibly via a sound tube secured in the auditory canal by means of an otoplastic material. The hearing aid and in particular the signal processing unit 3 are powered by a battery 5 likewise integrated in the hearing aid housing 1.
The interest in the present instance focuses on in-the-ear hearing aids where a plurality of microphones are employed for receiving sound signals. Using a plurality of microphones will ensure a directionality for the directional characteristic, which is to say a directional effect for the hearing aid.
Individually shaped shells of in-the-ear hearing aids can be produced especially quickly using what is termed rapid shell manufacturing (RSM) that employs electronic data indicating the shape of the shells. Microphones are for example positioned on a faceplate in the case of in-the-ear hearing aids. The necessary positioning data of the microphones, such as the distances between the microphone outputs, is made available to the RSM software. Because, though, a hearing aid shell is shaped individually and when worn is also oriented in a manner specific to the auditory canal, the faceplate is also oriented individually. How the microphones are positioned directly affects their directionality. The positioning data for any particular type of faceplate is, though, as a rule predefined on a non-customer-specific basis.
The publication DE 44 98 516 C2 discloses a gradient directional microphone system in which no more than three microphones are provided and a gradient order of an output signal referred to a common axis is at least two gradient orders higher than that of each of the microphones. In said gradient directional microphone system, a distance between two adjacent microphones is also taken into account.
The publication U.S. Pat. No. 6,879,697 B2 discloses a method for manufacturing a hearing aid including a hearing aid shell and a faceplate. The hearing aid is therein manufactured using CAD/CAM models.